The present invention relates to a bipolar electrode structure particularly suitable for use in fetal heart monitoring.
Various forms of monitoring electrode structures have been developed. These include, for example, a body organ electrode shown in U.S. Pat. No. 3,416,534 which is arranged for insertion into the body through a hypodermic needle and to function as a pacemaker electrode, and a similar type shown in U.S. Pat. No. 3,472,234. Both of these electrodes have a spiral configuration for attachment to a body organ. Other examples are the implantable electrode shown in U.S. Pat. No. 3,737,579, and the double spiral fetal electrode shown in U.S. Pat. No. 3,750,650.
A type of electrode to which the present invention is particularly directed is shown in greater detail in applicant's U.S. Pat. No. 3,890,420 and U.S. Pat. No. 3,910,271, and in FIGS. 8-10 of Hon U.S. Pat. No. Re. 28,990. FIG. 1 of the present application illustrates this form of prior art electrode which comprises a bipolar electrode formed by injection molding to form a body 12 having a first spiral electrode 13 at the forward end thereof and a second wafer electrode 14 at the rear end thereof. The first and second electrodes 13 and 14 are made of a conductive metal such as stainless steel or the like, and each is respectively connected to first and second insulated wire conductors 15 and 16. The exposed surface of the wafer electrode 14 generally is approximately twice the exposed surface area of the electrode 13. The other ends of the conductors 15 and 16 are connected in a manner well known in the art to electronic monitoring equipment (not shown) suitable for monitoring fetal heartbeat, heart rate or the like. U.S. Pat. No. 3,890,420 discloses a method and molding apparatus for forming the electrode structure of FIG. 1.
The spiral electrode of the type shown in FIG. 1 has been widely accepted and has overcome the various problems of the "forceps-endoscope" and the "sliding sleeve-clip" type of electrodes, both of which include clips but which must be squeezed onto the fetal epidermis. The spiral electrode of FIG. 1, on the other hand, can be readily easily inserted through the vagina and cervix of a woman in labor or about to be in labor by suitable applying devices of the nature shown in U.S. Pat. No. 3,910,271 and U.S. Pat. No. Re. 28,990 and, thus, in many instances can be quickly and effectively applied to the fetus during an early stage of labor, and which can be quickly and easily removed.
However, it has been found through years of use of the form of spiral electrode of the type shown in FIG. 1 that the doctor will apply one electrode by screwing into the fetal epidermis, but in many instances it comes off and a second one (and sometimes even more) must be applied. It generally is too cumbersome to attempt to reapply a first electrode which has become detached and, thus, that electrode usually is removed and another electrode applied. Because of the nature of the spiral, and the "lead" or angle of the spiral -3, there is a tendency for the spiral to unwind or unscrew itself spontaneously or inadvertently from the fetal scalp after being connected to the fetal scalp by the doctor. This not only necessitates one or more additional electrodes to be tried, but also results in undue trauma to the fetal scalp.
The present invention involves a modification of a portion of the spiral electrode of the type shown in FIG. 1 so as to provide improved frictional contact between a surface of the electrode and the fetal skin to thereby minimize the opportunity for the spiral to unwind itself. According to exemplary embodiments of the present invention, the surface of the spiral electrode which is to contact the fetal scalp is provided with protrusions in the form of, for example, points, ribs, ramps or the like to cause added friction or interference, or to gather scalp, so as to reduce or minimize the possibility for the spiral to unwind or unscrew spontaneously or inadvertently from the scalp.
Accordingly, it is a principal object of the present invention to provide an improved form of spiral electrode.
Another object of this invention is to provide a spiral electrode wherein the end that contacts skin is modified to increase the friction or interference between the electrode and the skin so as to minimize loosening or unwinding of the electrode from the skin.
A further object of this invention is to provide a new form of fetal monitoring spiral electrode having protrusions in the form of, for example, a plurality of points, ramps, ribs or the like, molded in the surface of the electrode which contacts the skin so as to minimize inadvertent detachment of the electrode from the skin.